Mammoth Cave developed in thick Mississippian-aged limestonestrata capped by a layer of sandstone, making the system remarkably stable. It is known to include more than 390 miles (630 km) of passageway;[5] new discoveries and connections add several miles to this figure each year. Mammoth Cave National Park was established to preserve the cave system.

The upper sandstone member is known as the Big Clifty Sandstone: thin, sparse layers of limestone interspersed within the sandstones give rise to an epikarstic zone, in which tiny conduits (cave passages too small to enter) are dissolved by the natural acidity of groundwater. The epikarstic zone concentrates local flows of runoff into high-elevation springs which emerge at the edges of ridges. The resurgent water from these springs typically flows briefly on the surface before sinking underground again at elevation of the contact between the sandstone caprock and the underlying massive limestones. It is in these underlying massive limestone layers that the human-explorable caves of the region have naturally developed.

Each of the primary layers of limestone is divided further into named geological units and subunits. One area of cave research involves correlating the stratigraphy with the cave survey produced by explorers. This makes it possible to produce approximate three-dimensional maps of the contours of the various layer boundaries without the necessity for test wells and extracting core samples.

The upper sandstone caprock is relatively hard for water to penetrate: the exceptions are where vertical cracks occur. This protective role means that many of the older, upper passages of the cave system are very dry, with no stalactites, stalagmites, or other formations which require flowing or dripping water to develop.

However, the sandstone caprock layer has been dissolved and eroded at many locations within the park, such as the Frozen Niagara room. The "contact" between limestone and sandstone can be found by hiking from the valley bottoms to the ridgetops: typically, as one approaches the top of a ridge, one sees the outcrops of exposed rock change in composition from limestone to sandstone at a well-defined elevation.[6]

At one valley bottom in the southern region of the park, a massive sinkhole has developed. Known as "Cedar Sink," the sinkhole features a small river entering one side and disappearing back underground at the other side.

The National Park Service offers several cave tours to visitors. Some notable features of the cave, such as Grand Avenue, Frozen Niagara, and Fat Man's Misery, can be seen on lighted tours ranging from one to six hours in length. Two tours, lit only by visitor-carried paraffin lamps, are popular alternatives to the electric-lit routes. Several "wild" tours venture away from the developed parts of the cave into muddy crawls and dusty tunnels. The lectures delivered by the National Park Service cave guides are varied by tour, so that in taking several tours the visitor learns about different facets of the cave's formation, or of the cave's human history and prehistory.

The Echo River Tour, one of the cave's most famous attractions, used to take visitors on a boat ride along an underground river. The tour was discontinued for logistic and environmental reasons in the early 1990s.[7]

The story of human beings in relation to Mammoth Cave spans six thousand years. Several sets of Native American remains have been recovered from Mammoth Cave, or other nearby caves in the region, in both the 19th and 20th centuries. Most mummies found represent examples of intentional burial, with ample evidence of pre-Columbian funerary practice.

An exception to purposeful burial was discovered when in 1935 the remains of an adult male were discovered under a large boulder. The boulder had shifted and settled onto the victim, a pre-Columbian miner, who had disturbed the rubble supporting it. The remains of the ancient victim were named "Lost John" and exhibited to the public into the 1970s, when they were interred in a secret location in Mammoth Cave for reasons of preservation as well as emerging political sensitivities with respect to the public display of Native American remains.

Research beginning in the late 1950s led by Patty Jo Watson of Washington University in St. Louis, Missouri has done much to illuminate the lives of the late Archaic and early Woodland peoples who explored and exploited caves in the region. Preserved by the constant cave environment, dietary evidence yielded carbon dates enabling Watson and others to determine the age of the specimens, and an analysis of their content, also pioneered by Watson, allows determination of the relative content of plant and meat in the diet of either culture over a period spanning several thousand years. This analysis indicates a timed transition from a hunter-gatherer culture to plant domestication and agriculture.

Another technique employed in archaeological research at Mammoth Cave was "experimental archaeology", in which modern explorers were sent into the cave using the same technology as that employed by the ancient cultures whose leftover implements lie discarded in many parts of the cave. The goal was to gain insight into the problems faced by the ancient people who explored the cave, by placing the researchers in a similar physical situation.

Ancient human remains and artifacts within the caves are protected by various federal and state laws. One of the most basic facts to be determined about a newly discovered artifact is its precise location and situation. Even slightly moving a prehistoric artifact contaminates it from a research perspective. Explorers are properly trained not to disturb archaeological evidence, and some areas of the cave remain out-of-bounds for even seasoned explorers, unless the subject of the trip is archaeological research on that area.

Besides the remains that have been discovered in the portion of the cave accessible through the Historic Entrance of Mammoth Cave, the remains of cane torches used by Native Americans, as well as other artifacts such as drawings, gourd fragments, and woven grass moccasin slippers are found in the Salts Cave section of the system in Flint Ridge.

The 31,000-acre (13,000 ha) tract known as the "Pollard Survey" was sold by indenture September 10, 1791 in Philadelphia by William Pollard. 19,897 acres (8,052 ha) of the "Pollard Survey" between the North bank of Bacon Creek and the Green River were purchased by Thomas Lang, Jr., a British American merchant from Yorkshire, England on June 3, 1796, for £4,116/13s/0d (£4,116.65). The land was lost to a local county tax claim during the War of 1812.

Legend has it that the first European to discover Mammoth Cave was either John Houchin or his brother Francis Houchin, in 1797. While hunting, Houchin pursued a wounded bear to the cave's large entrance opening near the Green River. Some Houchin Family tales have John Decatur "Johnny Dick" Houchin as the discoverer of the cave, but this is highly unlikely because Johnny Dick was only 10 years old in 1797 and was unlikely to be out hunting bears at such a tender age. His father John is the more likely candidate from that branch of the family tree, but the most probable candidate for discoverer of Mammoth Cave is Francis "Frank" Houchin whose land was much closer to the cave entrance than his brother John's. There is also the argument that their brother Charles Houchin, who was known as a great hunter and trapper, was the man who shot that bear and chased it into the cave. The shadow over Charles's claim is the fact that he was residing in Illinois until 1801. Contrary to this story is Brucker and Watson's The Longest Cave, which asserts that the cave was "certainly known before that time." Caves in the area were known before the discovery of the entrance to Mammoth Cave. Even Francis Houchin had a cave entrance on his land very near the bend in the Green River known as the Turnhole, which is less than a mile from the main entrance of Mammoth Cave.

The land containing this historic entrance was first surveyed and registered in 1798 under the name of Valentine Simons. Simons began exploiting Mammoth Cave for its saltpeter reserves.

According to family records passed down through the Houchin, and later Henderson families, John Houchin was bear hunting and the bear turned and began to chase him. He found the cave entrance when he ran into the cave for protection from the charging bear.

In partnership with Valentine Simon, various other individuals would own the land through the War of 1812, when Mammoth Cave's saltpeter reserves became significant due to the British blockade of United States's ports. The blockade starved the American military of saltpeter and therefore gunpowder. As a result, the domestic price of saltpeter rose and production based on nitrates extracted from caves such as Mammoth Cave became more lucrative.

In July 1812, the cave was purchased from Simon and other owners by Charles Wilkins and an investor from Philadelphia named Hyman Gratz. Soon the cave was being mined for calcium nitrate on an industrial scale.

A half-interest in the cave changed hands for ten thousand dollars (a huge sum at the time). After the war when prices fell, the workings were abandoned and it became a minor tourist attraction centering on a Native Americanmummy discovered nearby.

When Wilkins died his estate's executors sold his interest in the cave to Gratz. In the spring of 1838, the cave was sold by the Gratz brothers to Franklin Gorin, who intended to operate Mammoth Cave purely as a tourist attraction, the bottom long having since fallen out of the saltpeter market. Gorin was a slave owner, and used his slaves as tour guides. One of these slaves would make a number of important contributions to human knowledge of the cave, and become one of Mammoth Cave's most celebrated historical figures.

Stephen Bishop, an African-Americanslave and a guide to the cave during the 1840s and 1850s, was one of the first people to make extensive maps of the cave, and named many of the cave's features.

Stephen Bishop was introduced to Mammoth Cave in 1838 by Franklin Gorin. Gorin wrote, after Bishop's death: "I placed a guide in the cave – the celebrated and great Stephen, and he aided in making the discoveries. He was the first person who ever crossed the Bottomless Pit, and he, myself and another person whose name I have forgotten were the only persons ever at the bottom of Gorin's Dome to my knowledge.

"After Stephen crossed the Bottomless Pit, we discovered all that part of the cave now known beyond that point. Previous to those discoveries, all interest centered in what is known as the 'Old Cave' ... but now many of the points are but little known, although as Stephen was wont to say, they were 'grand, gloomy and peculiar'."[8]

The Mammoth Cave of Kentucky. An illustrated manual (1897)

In 1839, John Croghan of Louisville bought the Mammoth Cave Estate, including Bishop and its other slaves from their previous owner, Franklin Gorin. Croghan briefly ran an ill-fated tuberculosis hospital in the cave, the vapors of which he believed would cure his patients. A widespread epidemic of the period, tuberculosis would ultimately claim the lives of both Bishop and Croghan.

Throughout the 19th century, the fame of Mammoth Cave would grow so that the cave became an international sensation. At the same time, the cave attracted the attention of 19th century writers such as Robert Montgomery Bird, the Rev. Robert Davidson, the Rev. Horace Martin, Alexander Clark Bullitt, Nathaniel Parker Willis (who visited in June 1852), Bayard Taylor (in May 1855), William Stump Forwood (in spring 1867), the naturalist John Muir (early September 1867), the Rev. Horace Carter Hovey, and others.[9] As a result of the growing renown of Mammoth Cave, the cave boasted famous visitors such as actor Edwin Booth (his brother, John Wilkes Booth, assassinatedAbraham Lincoln in 1865), singer Jenny Lind (who visited the cave on April 5, 1851), and violinist Ole Bull who together gave a concert in one of the caves. Two chambers in the caves have since been known as "Booth's Amphitheatre" and "Ole Bull's Concert Hall".

By 1859, when the Louisville and Nashville Railroad opened its main line between these cities, Colonel Larkin J. Procter owned the Mammoth Cave Estate. He also owned the stagecoach line that ran between Glasgow Junction (Park City) and the Mammoth Cave Estate. This line transported tourists to Mammoth Caves until 1886, when he established the Mammoth Cave Railroad.

The difficulties of farming life in the hardscrabble, poor soil of the cave country influenced local owners of smaller nearby caves to see opportunities for commercial exploitation, particularly given the success of Mammoth Cave as a tourist attraction. The "Kentucky Cave Wars" were a period of bitter competition between local cave owners for tourist money. Broad tactics of deception were used to lure visitors away from their intended destination to other private show caves. Misleading signs were placed along the roads leading to the Mammoth Cave. A typical strategy during the early days of automobile travel involved representatives (known as "cappers") of other private show caves hopping aboard a tourist's car's running board, and leading the passengers to believe that Mammoth Cave was closed, quarantined, caved in or otherwise inaccessible.

In 1909, Max Kämper, a young German mining engineer, arrived at the cave by way of New York. Kämper had just graduated from technical college and his family had sent him on a trip abroad as a graduation present. Originally intending to spend two weeks at Mammoth Cave, Kämper spent several months. With the assistance of African-American slave descendant Ed Bishop, Kämper produced a remarkably accurate instrumental survey of many kilometers of Mammoth Cave, including many new discoveries. Reportedly, Kämper also produced a corresponding survey of the land surface overlying the cave: this information was to be useful in the opening of other entrances to the cave, as soon happened with the Violet City entrance.

The Croghan family suppressed the topographic element of Kämper's map, and it is not known to survive today, although the cave map portion of Kämper's work stands as a triumph of accurate cave cartography: not until the early 1960s and the advent of the modern exploration period would these passages be surveyed and mapped with greater accuracy. Kämper returned to Berlin, and from the point of view of the Mammoth Cave country, disappeared entirely. It was not until the turn of the 21st century that a group of German tourists, after visiting the cave, researched Kämper's family and determined his sad fate: the young Kämper was killed in trench warfare in World War I at the Battle of the Somme just seven years later, in 1916.

Famed French cave explorer Édouard-Alfred Martel visited the cave for three days in October 1912. Without access to the closely held survey data, Martel was permitted to make barometric observations in the cave for the purpose of determining the relative elevation of different locations in the cave. He identified different levels of the cave, and correctly noted that the level of Echo River within the cave was controlled by that of the Green River on the surface. Martel lamented the 1906 construction of the dam at Brownsville, pointing out that this made a full hydrologic study of the cave impossible. Among his precise descriptions of the hydrogeologic setting of Mammoth Cave, Martel offered the speculative conclusion that Mammoth Cave was connected to Salts and Colossal Caves: this would not be proven correct until 60 years after Martel's visit.[10]

In the early 1920s, George Morrison blasted a number of entrances to Mammoth Cave on land not owned by the Croghan Estate. Absent the data from the Croghan's secretive surveys, performed by Kämper, Bishop, and others, which had not been published in a form suitable for determining the geographic extent of the cave, it was now conclusively shown that the Croghans had been for years exhibiting portions of Mammoth Cave which were not under land they owned. Lawsuits were filed and for a time, different entrances to the cave were operated in direct competition with each other.

In the early 20th century, Floyd Collins spent ten years exploring the Flint Ridge Cave System (the most important legacy of these explorations was the discovery of Floyd Collins' Crystal Cave and exploration in Salts cave) before dying at Sand Cave, Kentucky, in 1925. While exploring Sand Cave, he dislodged a rock onto his leg while in a tight crawl way and was unable to be rescued before dying of starvation.[11] Attempts to rescue Collins created a media sensation: The resulting publicity would draw prominent Kentuckians to initiate a movement which would soon result in the formation of Mammoth Cave National Park.

Visitors on a tour of Mammoth Cave descend the stairs of the Historic (or Houchins) entrance.

As the last of the Croghan heirs died, advocacy momentum grew among wealthy citizens of Kentucky for the establishment of Mammoth Cave National Park. Private citizens formed the Mammoth Cave National Park Association in 1926. The Park was authorized May 25, 1926.

Donated funds were used to purchase some farmsteads in the region, while other tracts within the proposed National Park boundary were acquired by right of eminent domain. In contrast to the formation of other National Parks in the sparsely populated American West, thousands of people would be forcibly relocated in the process of forming Mammoth Cave National Park. Often eminent domain proceedings were bitter, with landowners paid what were considered to be inadequate sums. The resulting acrimony still resonates within the region.[citation needed]

For legal reasons, the federal government was prohibited from restoring or developing the cleared farmsteads while the private Association held the land: this regulation was evaded by the operation of "a maximum of four" CCC camps from May 22, 1933 to July 1942.[12][13]

According to the National Park Service,[14] "On May 14, 1934 the minimum park area was provided. On May 22, 1936, the minimum area was accepted "for administration and protection."[citation needed]

Superintendent Hoskins later wrote of a Summer Tanager named Pete who arrived at the guide house on or around every April 20, starting in 1938. The bird ate from food held in the hands of the guides, to the delight of visitors, and provided food to his less-tame mate.[15]

Mammoth Cave National Park was officially dedicated on July 1, 1941. By coincidence, the same year saw the incorporation of the National Speleological Society. R. Taylor Hoskins, the second Acting Superintendent under the old Association, became the first official Superintendent, a position he held until 1951.

The New Entrance, closed to visitors since 1941, was reopened on December 26, 1951, becoming the entrance used for the beginning of the Frozen Niagara tour.[16]

By 1954, Mammoth Cave National Park's land holdings encompassed all lands within its outer boundary with the exception of two privately held tracts. One of these, the old Lee Collins farm, had been sold to Harry Thomas of Horse Cave, Kentucky, whose grandson, William "Bill" Austin, operated Collins Crystal Cave as a show cave in direct competition with the National Park, which was forced to maintain roads leading to the property. Condemnation and purchase of the Crystal Cave property seemed only a matter of time.

In February 1954, a two-week expedition under the auspices of the National Speleological Society was organized at the invitation of Austin: this expedition became known as C-3, or the Collins Crystal Cave Expedition.[17]

The C-3 expedition drew public interest, first from a photo essay published by Robert Halmi in the July 1954 issue of True Magazine and later from the publication of a double first-person account of the expedition, The Caves Beyond: The Story of the Collins Crystal Cave Expedition by Joe Lawrence, Jr. (then president of the National Speleological Society) and Roger Brucker. The expedition proved conclusively that passages in Crystal Cave extended toward Mammoth Cave proper, at least exceeding the Crystal Cave property boundaries. However, this information was closely held by the explorers: it was feared that the National Park Service might forbid exploration were this known.[18]

In 1955 Crystal Cave was connected by survey with Unknown Cave, the first connection in the Flint Ridge system.

Some of the participants in the C-3 expedition wished to continue their explorations past the conclusion of the C-3 Expedition, and organized as the Flint Ridge Reconnaissance under the guidance of Austin, Jim Dyer, John J. Lehrberger and E. Robert Pohl. This organization was incorporated in 1957 as the Cave Research Foundation. The organization sought to legitimize the cave explorers' activity through the support of original academic and scientific research. Notable scientists who studied Mammoth Cave during this period include Patty Jo Watson (see section on prehistory.)

In March 1961, the Crystal Cave property was sold to the National Park Service for $285,000.[19] At the same time, the Great Onyx Cave property, the only other remaining private inholding, was purchased for $365,000. The Cave Research Foundation was permitted to continue their exploration through a Memorandum of Understanding with the National Park Service.

Colossal Cave was connected by survey to Salts Cave in 1960 and in 1961 Colossal-Salts cave was similarly connected to Crystal-Unknown cave, creating a single cave system under much of Flint Ridge. By 1972, the Flint Ridge Cave System had been surveyed to a length of 86.5 miles (139.2 km), making it the longest cave in the world.

River Styx, one of the cave's semi-subterranean waterways, emerges onto the surface in the park.

During the 1960s, Cave Research Foundation (CRF) exploration and mapping teams had found passageways in the Flint Ridge Cave System that penetrated under Houchins Valley and came within 800 feet of known passages in Mammoth Cave. In 1972, CRF Chief Cartographer John Wilcox pursued an aggressive program to finally connect the caves, fielding several expeditions from the Flint Ridge side as well as exploring leads in Mammoth Cave.

On a July 1972 trip deep in the Flint Ridge Cave System, Patricia Crowther—with her slight frame of 115 pounds (52 kg)—crawled through a narrow canyon later dubbed the "Tight Spot", which acted as a filter for larger cavers. A subsequent trip past the Tight Spot on August 30, 1972 by Wilcox, Crowther, Richard Zopf, and Tom Brucker discovered the name "Pete H" inscribed on the wall of a river passage with an arrow pointing in the direction of Mammoth Cave.[20] The name is believed to have been carved by Pete Hanson, who was active in exploring the cave in the 1930s. Hanson had been killed in World War II. The passage was named Hanson's Lost River by the explorers.

Finally, on September 9, 1972, a six-person CRF team of Wilcox, Crowther, Zopf, Gary Eller, Stephen Wells, and Cleveland Pinnix (a National Park Service ranger) followed Hanson's Lost River downstream to discover its connection with Echo River in Cascade Hall of Mammoth Cave. With this linking of the Flint Ridge and Mammoth Cave systems, the "Everest of speleology" had been climbed. The integrated cave system contained 144.4 miles (232.4 km) of surveyed passages and had fourteen entrances.[21]

Further connections between Mammoth Cave and smaller caves or cave systems have followed, notably to Proctor/Morrison Cave beneath nearby Joppa Ridge in 1979. Proctor cave was discovered by Jonathan Doyle, a Union army deserter during the Civil war, and was later owned by the Mammoth cave railroad, before being explored by the CRF. Morrison cave was discovered by George Morrison in the 1920s. This connection pushed the frontier of Mammoth exploration southeastward.

River Styx

At the same time, discoveries made outside the Park by an independent group called the Central Kentucky Karst Coalition or CKKC resulted in the survey of tens of miles in Roppel Cave east of the Park. On September 10, 1983, a connection was made between the Proctor/Morrison's section of the Mammoth Cave system and Roppel Cave. The connection was made by two mixed parties of CRF and CKKC explorers. Each party entered through a separate entrance and met in the middle before continuing in the same direction to exit at the opposite entrance. The resulting total surveyed length was near 300 miles (480 km).

On March 19, 2005, a connection into the Roppel Cave portion of the system was surveyed from a small cave under Eudora Ridge, adding approximately three miles to the known length of the Mammoth Cave System. The newly found entrance to the cave, now termed the "Hoover Entrance," had been discovered in September, 2003, by Alan Canon and James Wells.[22] Incremental discoveries since then have pushed the total to 400 miles (640 km).[3][5]

It is certain that many more miles of cave passages await discovery in the region. Discovery of new natural entrances is a rare event: the primary mode of discovery involves the pursuit of side passages identified during routine systematic exploration of cave passages entered from known entrances.

Two other massive cave systems lie short distances from Mammoth Cave: the Fisher Ridge Cave System and the Martin Ridge Cave System. The Fisher Ridge Cave System was discovered in January 1981 by a group of Michigan cavers associated with the Detroit Urban Grotto of the National Speleological Society.[citation needed] So far, the cave has been mapped to 117 miles (188 km).[5] In 1976, Rick Schwartz discovered a large cave south of the Mammoth Cave Park boundary. This cave became known as the Martin Ridge Cave System in 1996 as new exploration connected the nearby caves of Whigpistle Cave (Schwartz's original entrance), Martin Ridge Cave, and Jackpot Caves. As of December 2008, the Martin Ridge Cave System is mapped to a length of 34 miles (55 km), and exploration continues.[citation needed]

All together, these and more rare bat species such as the Eastern Small-footed Bat had estimated populations of 9–12 million just in the Historic Section. While these species still exist in Mammoth Cave, their numbers are now no more than a few thousand at best. Ecological restoration of this portion of Mammoth Cave, and facilitating the return of bats, is an ongoing effort. Not all bat species here inhabit the Cave; the red bat (Lasiurus borealis) is a forest-dweller, found underground only rarely.

No fossils of the woolly mammoth have ever been found in Mammoth Cave, and the name of the cave has nothing to do with this extinct mammal. Rather, the name "Mammoth" refers to the large width and length of the passages connecting to the Rotunda just inside the entrance.[23] This name was given long before the cave system's true extent was fully known. Modern discoveries have proven the aptness of the name.

The layout for one of the earliest computer games, Colossal Cave Adventure, was based partly on the Mammoth cave system.

H.G. Wells' The Time Machine refers to the "bleached look common in most animals that live largely in the dark--the white fish of the Kentucky caves, for instance."

A significant amount of the work of American poet Donald Finkel stems from his experiences caving in Mammoth Cave National Park. Examples include "Answer Back," from 1968, and the book-length "Going Under," published in 1978.

Hovey, Horace Carter (Hovey 1880) One Hundred Miles in Mammoth Cave in 1880: an early exploration of America's most famous cavern. with introductory note by William R. Jones. Golden, Colorado: Outbooks. (Copyright 1982) ISBN 0-89646-054-1

Roger W. Brucker has co-authored four nonfiction books and authored one historical novel on the history and exploration of the Mammoth Cave System. They are presented here not in the order of publication, but in the order in which the events of the books' major narratives took place:

Brucker, Roger W. (2009) Grand, Gloomy, and Peculiar: Stephen Bishop at Mammoth Cave. Cave Books. ISBN 978-0-939748-72-3 (hbk) ISBN 978-0-939748-71-6 (pbk). Based on the true story of Stephen Bishop, the slave who gained fame as a guide and explorer at Mammoth Cave from 1838 until his death in 1857, this historical novel is written from the perspective of Bishop's wife, Charlotte. Although it is a novel, Brucker has claimed the book does not alter any known historical facts.

Brucker, Roger W. and Murray, Robert K. (Brucker and Murray 1983) Trapped: The Story of Floyd Collins. University of Kentucky Press. Told by a scholar of early 20th century journalism and a veteran of the modern period of Mammoth Cave exploration, this book details the events of the entrapment and attempted rescue of Floyd Collins, who was trapped in a cave near Mammoth Cave in January 1925.

Lawrence, Jr, Joe and Brucker, Roger W. (Lawrence and Brucker 1955) The Caves Beyond: The story of the Floyd Collins' Crystal Cave Expedition New York: Funk and Wagnalls. Reprinted, with new introduction, by Zephyrus Press ISBN 0-914264-18-4 (pbk.) Details the story of the 1954 week-long C3 expedition from the separate points of view of the leader and an ordinary participant in the expedition, who went on to become one of the leaders of the then-nascent modern period of exploration.

Brucker, Roger W. and Watson, Richard A. "Red" (Brucker and Watson 1976) The Longest Cave. New York : Knopf (reprinted 1987, with afterword: Carbondale, Illinois: Southern Illinois University Press) ISBN 0-8093-1322-7 (pbk.) A comprehensive story of the exploration of Mammoth Cave told by two of the founders of the Cave Research Foundation. An invaluable appendix, "Historical Beginnings", outlines the story of the cave from prehistory to the mid-1950s, where the main narrative begins. The formation of the Cave Research Foundation is described from an insider perspective. A highly personal telling, this work is sometimes jokingly or with irony referred to by cavers as Roger and Red Go Caving, though its revered status in the literature and the reputations of the authors are hardly in doubt. The 1989 reprint includes an Afterword by the authors referring to the 1983 Roppel-Mammoth connection and other subsequent events.

Borden, James D. and Brucker, Roger W. (Borden and Brucker 2000) Beyond Mammoth Cave: A Tale of Obsession in the World's Longest Cave. Carbondale and Edwardsville, Illinois: Southern Illinois University Press. ISBN 0-8093-2346-X. Taking up where The Longest Cave leaves off, carries the story of Mammoth Cave Exploration from September 10, 1972 to September 10, 1983, when a connection was surveyed between Roppel Cave and the southern reaches of Mammoth Cave. Details the origins of the Central Kentucky Karst Coalition (CKKC).

Watson, Patty Jo (ed.) (Watson 1974) Archaeology of the Mammoth Cave Area. Reprinted 1997 by St. Louis: Cave Books ISBN 0-939748-41-X. 31 chapters by the foremost worker in the field of Mammoth Cave archaeology and several of her colleagues. The reprinted edition includes a brief new introduction and a brief updated bibliography.

Livesay, Ann, and McGrain, Preston (revised) (Livesay and McGrain 1962). Geology of the Mammoth Cave National Park Area. Kentucky Geological Survey, Series X, 1962. Special Publication 7, College of Arts and Sciences, University of Kentucky. Lexington, Kentucky: University of Kentucky.

Palmer, Arthur N. (Palmer 1981) A Geological Guide to Mammoth Cave National Park. Teaneck, New Jersey: Zephyrus Press. ISBN 0-914264-28-1. 196 pp. From the "blurb" on the back cover: "How did Mammoth Cave form? How old is it? Why does it look the way it does? What do the rocks tell us? These and many other questions are answered in this book about America's most popular cave." Written for the lay reader, but with much technical information of interest to those with greater scientific literacy, by a retired professor of geology at SUNY Oneonta.